(1) Field of the Invention
The present invention relates to devices utilized in semiconductor production processes. More specifically, the present invention relates to wafer support devices.
(2) Description of the Related Art
In the course of forming integrated circuit structures on semiconductor wafers, certain processes are utilized that involve the use of heated susceptors or wafer supports located in enclosed chambers where these processes take place. Some of these processes include, for example, growth of an epitaxial silicon layer, the formation of a thermal oxide or thermal nitride layer over silicon, the rapid thermal annealing of integrated circuit structures already formed on the wafer, etc. Typically, devices such as susceptors, susceptor supports, and wafer supports may be used for supporting the wafers horizontally from below.
FIG. 1 illustrates an assembly 100 for supporting a semiconductor wafer 104. Assembly 100 includes a susceptor 102 upon which semiconductor wafer 104 may be placed and supported horizontally. Susceptor 102 is typically supported by susceptor support 108 which includes a shaft 116 with three susceptor arms 109 that outwardly extend therefrom along directions positioned at 120.degree. relative to one another. The susceptor support 108 further includes three legs 110. Each of legs 110 upwardly extends from a corresponding remote end of susceptor arm 109 to engage a bottom surface of susceptor 102 thereby supporting susceptor 102. Moreover, susceptor support 108 includes a central leg 117 that upwardly extends from shaft 116 to center susceptor 102.
Susceptor 102 includes three through-holes 113 formed therethrough at three locations that are positioned at 120.degree. relative to one another on a circle that has a diameter smaller than a diameter of wafer 104. Three lift pins 112 that support wafer 104 are mounted through the three holes 113 of susceptor 102 of the assembly 100 for supporting wafer 104. FIG. 1 shows wafer 104 supported by lift pins 112 in a position where wafer 104 is displaced from susceptor 102 to allow a robot arm 103, placed between wafer 104 and susceptor 102, to insert or remove wafer 104 to/from assembly 100. A displacement between wafer 104 and susceptor 102 may be created by moving the susceptor support 108 downwards relative to wafer 104 while maintaining wafer 104 fixed at the same position.
The three holes 113 of susceptor 102 may have an upper portion that is tapered, with a gradual increasing diameter, positioned adjacent to an upper surface of the susceptor 102. A tapered section with gradually increasing diameter is also formed at an upper end of the lift pins 112. This tapered section is conformed to fit in the tapered section of the through-holes 113 so that lift pins 112 may be stopped at the susceptor level when the wafer 104 is placed directly upon the susceptor thereby preventing lift pins 112 from dropping passed the susceptor.
Lift pins 112 are typically installed from the top by dropping them through susceptor 102's through-holes 113 and through through-holes 115 of susceptor support arms 109. The installation of lift pins 112 is difficult as susceptor 102 is made of graphite, which is opaque, and which makes it practically impossible to see the through-holes 115 of susceptor arms 109 from above the susceptor, once pins 112 are inserted through through-holes 113.
Typically, susceptor 102 and wafer 104, that may be mounted thereon, are located in a sealed processing chamber (not shown) such as a double domed chamber (not shown), for example, where these devices may be heated by a plurality of heating devices (heat lamps) symmetrically arranged below the susceptor in the chamber, as well as over wafer 104. Heat from the heat lamps radiates through the dome to the underside of the susceptor to heat susceptor 102 as well as wafer 104 that may be positioned thereon. The wafer is also heated by a second set of heat lamps situated above an upper dome positioned over the wafer and the susceptor.
A use of central leg 117, that centers susceptor 102, in conjunction with the heating performed by the heat lamps may result in uneven distribution of heat across susceptor 102. This is caused by thermal coupling of the central portion of susceptor 102 to shaft 116 via central leg 117 as well as uneven distribution of heat radiating from the heat lamps to the susceptor 102 due to shadowing of the under side of susceptor 102 by central leg 117. Such uneven heating, or thermal non-uniformity, of susceptor 102 may further result in uneven heating of wafer 104.
The wafer support device shown in FIG. 1 further may include a wafer lift device that has three wafer lift arms 120 outwardly extending from wafer central lift 122. The wafer lift arms 120 may typically be integral with the wafer central lift 122. This design is disadvantageous as it requires replacement of the entire wafer lift device (the wafer lift arms 120 and the wafer central lift 122), when a wafer that has a different diameter is processed. Another disadvantage of this design, is that movement of susceptor support 108 in a downward direction is limited by wafer lift arms 120 thereby limiting the displacement that may be provided between wafer 104 and susceptor 102. Yet another disadvantage is that wafer lift arms 120 with pads 123 that support pins 112 create shadowing due to their position.
Furthermore, susceptor support 108 with arms 109 may be rotated by a rotation mechanism that may be installed at the lower part of shaft 116. When such rotation occurs wafer lift arms 120 and wafer central lift 122 are kept stationary. Such configuration requires that when shaft 116 is rotated a rotation mechanism is installed on the susceptor on the shaft at a position that ensures that when the rotation of the shaft 116 is terminated, the arms 109 guiding pins 112 are stopped at a position where these arms are aligned with wafer lift arms 120 such that a bottom part of pins 112 coincides with pads 123. Such exact installation of the rotation mechanism is limiting and undesirable.
It is desirable to provide a wafer support device with a susceptor support that permits more even heating and thermal uniformity or heat distribution across the susceptor and thereby more even heating or heat distribution across the semiconductor wafer being processed. It is also desirable to provide a wafer support device where the central wafer lift does not need to be changed with every wafer that has a different size. Also, it is desirable to provide a wafer support that does not interfere with the adjustment of the susceptor support.